In recent years, breast cancer among women has become an increasingly serious problem. Palpation, ultrasonic image diagnosis and mammography are used for determination of the presence of a cancer of the breast. In particular, the usefulness of mammography with a fluorescent screen is becoming clear. In older mammography techniques, an X-ray film for industrial use was used to form an image directly with an X-ray but there have been the problems with this method from excessive radiation exposure and accumulation.
Mammography with a fluorescent screen has an exposure of 1/10th to 1/100th that resulting from the methods for forming an image directly with an X-ray and is very effective for reducing exposure. Therefore, it is becoming the most effective technique for detection of a cancer of the breast.
The problem with mammography with a fluorescent screen is inferior resolution. The cause thereof is an image which is fuzzed due to interception by the screen and a reduced exposure of an X-ray to increase the quantum mottle and lower the S/N ratio. Particularly in photographing a breast, a very small absorption difference of an X-ray due to a tissue change to a morbid state has to be turned into an image and a very small change to a morbid state of a fine line image has to be turned into an image, so that this reduction of the S/N ratio is a very important problem.
Various attempts have been made in order to improve resolution. In an X-ray generation device, it has been tried to turn an X-ray into a homogeneity by a molybdenum filter with a molybdenum target. In a fluorescent screen, high density loading of a fluorescent substance has been tried and adhesiveness to a film has been improved by providing the screen surface with a matting property to improve sharpness. Also, in a cassette, a carbon resin is used, so that its strength is compatible with a thinner thickness and the loss of an X-ray due to absorption thereof by the cassette has been reduced.
Various light-sensitive materials are offered so that the relationship between sensitivity and resolution may be improved.
Various improvements have been tried but the relationship between sensitivity and resolution has not yet been satisfactorily determined.
Conventional light-sensitive materials for photographing a breast are roughly classified as a low gamma type represented by (a) or a high gamma type represented by (b) in the characteristic curve of FIG. 1. In the low gamma type of (a), much information is available from the low exposure portion to the high exposure portion, but it is difficult to perceive the contrast and therefore to make a diagnosis. In the high gamma type of (b), contrast is excellent and the image needed to make a diagnosis can be obtained. However, in the high exposure portion, it is difficult to make a diagnosis because the density is too high.
In the image required for photographing a breast, a very small absorption difference in an X-ray attributable to a change to a morbid state of a mammary gland in the breast has to be turned into an image by giving contrast and at the same time, the skin line of the breast has to be clearly pictured. The low gamma type of (a) is suited to picturing the skin line. However, it has a high possibility of missing a change to a morbid state because a very small absorption difference can not be emphasized by giving contrast. On the contrary, the high contrast type of (b) is suited to picturing the inside of a breast, but the skin line can not be pictured without using a high luminance sharcastein because the densities of the skin line and back are too high.
Also, in a light-sensitive material, not only improvement in the relationship between sensitivity and resolution, but also improvement in handling properties are important factors. That is, there are various problems generated in handling, for example, pressure sensitization and desensitization, color stain of a processed light-sensitive material, residual silver, and discolorination by hypo after storage over a long period of time.
An X-ray light-sensitive material for photographing a breast is susceptible to pressure blackening and pressure desensitization marks because the light-sensitive material is folded by its own weight when it is loaded into a cassette and because mechanical force is exerted on it in an automatic exposing device or developing device in which mechanical transportation is used. Such troubles are likely to leading to serious problems in a medical diagnosis.
Various attempts at changing the physical properties of light-sensitive materials have been tried for the purpose of improving pressure sensitization and desensitization. The descriptions thereof can be found in, for example, U.S. Pat. Nos. 3,536,491, 3,775,128, 3,003,878, 2,759,821, and 3,772,032, and JP-A-53-3325 (the term "JP-A" as used herewith means an unexamined Japanese patent application), JP-A-50-56227, JP-A-50-147324, and JP-A-51-141625. In these techniques, however, while pressure desensitization is improved, deterioration of the physical properties of the binder, such as its adhesiveness, drying property and film surface scratching property, is notable and can not basically be improved.
Further, there are available as additives, the inorganic salts of chlorine and typical elements described in JP-A-2-6803, and polyhydroxybenzenes disclosed in JP-A-1-72141. In any case, however, a sufficient improvement has not yet been achieved.
An improvement in the pressure property of a silver halide emulsion itself has variously been tried. It is well known in the art that in general, solid silver halide grains having a large grain size are susceptible to pressure desensitization and that tabular grains are susceptible to transformation with pressure and generation of a pressure blackening.
Meanwhile, there is an intense need to shorten the processing time of an X-ray light-sensitive material for photographing a breast. The medical detection of a breast cancer is getting popular and the persons to be examined are increasing. Further, in a medical examination, at least 4 photographs per one person are usually taken, and therefore it is desired to process a high number of light-sensitive materials in as short time as possible.
A sensitizing dye remains when the processing time is shortened and a color stain is likely to generate. Further, silver and hypo are likely to remain and discoloration is likely to take place after storage over a long period of time. The solution of these various problems would benefit users very much.